1. Field of the Invention
The present invention relates to a passive coherent location (xe2x80x9cPCLxe2x80x9d) radar system and method, and more particularly, to a system and method for detection and feature extraction for PCL radar applications.
2. Discussion of the Related Art
PCL radar systems may be represented by a multistatic radar system. A multistatic radar system has many receivers that are separated from one or more transmitters. The radiated signal from a transmitter arrives at a receiver via two separate paths. One path may be a direct path from the transmitter to the receiver, and the other path may be a target path that includes an indirect path from the transmitter to a target to the receiver. Measurements may include a total path length, or transit time, of the target path signal, the angle of arrival of the target path signal, and the frequency of the direct and target path signals. A difference in frequency may be detected according to a doppler effect if the target is in motion.
Knowledge of the transmitted signal is desirable at the receiver if information is to be extracted from the target path signal. The transmitted frequency is desired to determine the doppler frequency shift. A time or phase reference also is desired if the total scattered path length is to be determined. The frequency reference may be obtained from the direct signal. The time reference also may be obtained from the direct signal provided the distance between the transmitter and the receiver is known.
Multistatic radar systems may be capable of determining the presence of a target within the coverage of the radar, the location of the target position, and a velocity component, or doppler, relative to the radar. The process of locating the target position may include a measurement of a distance and the angle of arrival. The measurement determination of distance relative to the receiving site may require both the angle of arrival at the receiving site and the distance between transmitter and receiver. If the direct signal is available, it may be used as a reference signal to extract the doppler frequency shift.
In PCL radar systems, transmitters may be known as illuminators. Illuminators may be wideband sources of opportunities that include commercial frequency modulated (xe2x80x9cFMxe2x80x9d) broadcast transmitters and/or repeaters, commercial high-definition television (xe2x80x9cHDTVxe2x80x9d) broadcast transmitters and/or repeaters, and the like. Known techniques for wideband signal pre-detection processing and co-channel interference mitigation exist. Known approaches include an array of antennas used to receive the source of opportunity to be exploited, such as the primary illuminator, and any other co-channel signals present in the environment.
After the received signals have been processed, target parameters should be extracted and new targets detected. Existing targets may be updated with the data for the current processing interval. The detection and feature extraction of target information should be performed in an accurate and timely manner. Incorrect or invalid detections may waste processing resources and require additional computing. Further, a system should detect new targets without false alarms from noise or ground clutter. Thus, a PCL radar system should be able to detect targets and extract features of those targets in an efficient and accurate manner
Accordingly, the present invention is directed to PCL applications and signal processing within the PCL application.
According to an embodiment, a method for detecting and extracting target information during a coherent processing interval within a passive coherent location system is disclosed. The method includes forming an ambiguity surface having ambiguity surface data for the coherent processing interval. The method also includes identifying bins from a previous ambiguity surface. The method also includes associating the bins from the previous ambiguity surface with the ambiguity surface data. The method also includes identifying new bins for new target echoes within the ambiguity surface.
According to another embodiment, a method for detecting and extracting target data for targets within a coherent processing interval in a passive coherent location system is disclosed. The method includes generating an ambiguity surface. The method also includes associating bins with the ambiguity surface. The method also includes forming peak detections from the bins. The peak detections correlate to target echoes within the coherent processing interval. The method also includes estimating targets parameters from the peak detections.
According to another embodiment, a method for extracting target parameters of potential targets from ambiguity surface data of an ambiguity surface in a passive coherent location system is disclosed. The ambiguity surface data correlates to a coherent processing interval and with echoes of the potential targets. The method includes retrieving a previous ambiguity surface. The method also includes comparing the ambiguity surface data with the previous ambiguity surface to identify bins associated with known targets. The method also includes updating the bins with the ambiguity surface data. The method also includes identifying new bins for new target echoes of the potential target echoes. The method also includes grouping the bins and the new bins into peak detections. The method also includes estimating the target parameters for the potential targets from the peak detections.
According to another embodiment, a system for detecting and extracting features of potential targets from an ambiguity surface for a coherent processing interval in a passive coherent location system is disclosed. The system includes an ambiguity surface formation function performing the ambiguity surface and generating the ambiguity surface data. The system also includes a peak/noise discrimination function for identifying bins for known targets and new targets with the ambiguity surface data. The system also includes a peak association function for grouping the bins to determine peak detections associated with the known and new targets. The surface also includes a parameter estimation function for estimating target parameters for the known and new targets from the peak detections. The system also includes a peak editing function for editing the peak detections.
According to another embodiment, a method for detecting and extracting features for targets identified by a passive coherent location system is disclosed. The method includes associating bins with an ambiguity surface data. The method also includes forming peak detections from the bins.
According to another embodiment, a passive coherent location radar system having a detection and feature extraction processing subsystem to detect targets and determine target parameters from ambiguity surface data of an ambiguity surface is disclosed. The passive coherent location radar system includes a peak/noise discriminator to compare previous ambiguity surface data to the ambiguity surface data and to update bins correlating to the previous ambiguity surface data. The passive coherent location radar system also includes new bins identified by the peak/noise discriminator for new target echoes within the ambiguity surface. The passive coherent location radar system also includes a peak associator to group the bins and the new bins identified by the peak/noise discriminator to form peak detections correlating to the targets. The passive corherent location radar system also includes a parameter estimator to estimate the target parameters from the peak detections.
Additional features and advantages of the invention will be set forth in the description, which follows, and in part will be apparent from the description, or maybe learned, by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.